Method of recovering alumina from alumina-bearing ores



WANN

R. C. HAFF AFiled April 19, 1947 IN1 WAVE METHOD oF RECOVERING ALUMINA FROM ALUMINA BEARING omlzs May 8, 1951 A /NVE/VTOR ATTORNEY Patented May 8, 1951 UNITED STATES PATENT OFFICE` METHOD OF RECOVERING ALUMINA FROM I ALUMINA-BEARING GRES Robert C. Half, Latrobe, Pa.

Application April 19, 1947, Serial No. 742,676

(Cl. .Z3-141) 2 lClaims. 1

This invention relatesto method of and apparatus for treating alumina bearing ores and the like, and it is among the objects thereof to provide a method of treating alumina bearing ores to separate the valuable products in their commercially pure state.

The invention is especially adapted for treating clay ores, feldspar, diaspore, eyanite, bauxites, the red mud wastes of the Bayer Process for bauxite, alums, alunite, bentonite, shales and other alumina bearing ores; also the processv may be employed for the recovery of alumina oxide and vanadium oxide and the like from slags such as iron, vanadium and chromium slags.

The present invention is a modification of and in some respects an improvement on the method of treating aluminum compounds disclosed in my Patent No. 2,398,425, granted April 16', 1946.

The invention will become more apparent from a consideration of the accompanying drawing, constituting a part hereof, in which like reference characters designate like parts, and in which Figi is a View diagrammatically illustrating apparatus carrying out my improved method of treating alumina ores; and

Fig. 2 a cross sectional view taken along the line 2--2, Fig. 1.

Clay or other alumina bearing bodies are crushed in a crusher I and then ground in grinders 2 and fed by a feed hopper 9 to a rotary calcining kiln 4 wherein it is heated at a temperature between 300 C. to 900 C. to prepare the ore for digestion in vats 5 by adding from 30% to concentrated solution of sulphuric acid (H2504), or other suitable acids, to change the insoluble aluminum oxide (A1203) to soluble aluminum sulphate (A12(SO4)3). By this step any iron or titanium oxides present are changed to soluble sulphates. IIhe digested product is then passed as a solid to a Crusher 6 and .thence to the feed hopper 1 of another kiln or it is passed as a slurry to the second kiln, generally designated by the numeral 8. The latter kiln can be red from either end. The fuel used for burning can be added with the material at the hopper 'l or at the discharge end of kiln 8. When alunite or any alumina bearing ores containing S03 are heated in kiln 4 they are caught in the stack chamber Yand put into tank 9. Should any potassium or sodium compounds be present between discharge end of tank 4 and the digestion vat they are leached out before digestion.

In the digesting step after calcining in the kiln 4, therH2O added is preferably of 66 B.

2 which contains approximately 93.19% I-I2S04 or 76.07% S03 at a specic gravity of 1.8354 at F. At a temperature of 70 F., which is room temperature, the B. of I-I2S04 is 65.75 with approximately 92.10% I-I2S04 or 75.19% S03 and a specic gravity of 1.8300. As each part of the A1203 requires 2.355 parts of S03 to form Al2(S04) s, each part of A1203 requires 3.10 parts of I-I2S04 at 1.8300 specific gravity at 70 F. In liquid measure this would be 1.7 parts H2804 at a temperature of F. for each part of A1203 by weight. I do not wish to be limited to the use of concentrated H2S04 at 66 B., as I havev used weaker H2S04 with a B. of 27 and specific gravity of 1.229 at 60 F. If a weaker acid is used, the amount should be so that there is sufcient S03 in the proportion of 2.355 parts S03 to one part of A1203, and also sufficient S03 to change the iron and titanium to sulphates. Also when weaker acids are used the time of the digestion is prolonged on account of the evaporation of the excess water present.

Should an excess I-I2SO4 be present after digestion of the A1203 in the calcine, I may add more calcine material so that all the S03 present, in.

the excess acid combines with the A1203 in the added calcine and forms A12(S04)3. The calcine may be added to either hot or cold acid solutions and the acid may be added to hot or cold calcine.

A slight amount of heat is used to start thev digestion which causes a somewhat violent re` action as the A1203 and S03 combine to formV Al2(S04)3. During the reaction the temperature stays below 300 C. The more concentrated the acid used the more violent the reaction and the higher the temperature, which, however, is always below 300 C. At a 30% strength of H2S04, the temperature during the reaction is about C. By the use of concentrated H2S04, the reaction may take place 15 to 20 minutes, but when a 30% solution is used the reaction may take one hour or longer. The heating of the mass is continued until it becomes a solid mass and white fumes, S03, are driven off. These fumes appear when excess H2S04 is used.

The result of the digestion of the calcined material treated in the kiln l is that if the calcine contains either iron or titanium oxide they would be converted to Fe2(S04)3 and Ti2(S04)3. The aluminum and iron sulphate are dissolved by the addition of suicent water and heated and the Ti2(S04) 3 will also be dissolved if a slight amount of H2S04 is present, which there usually is. If

small amounts of potassium or sodium com.

pounds are present in the calcine in some form, such as in combination with alumina and silica, they would form an insoluble potassium or sodium alumina silicate which has the same composition as Feldspars, and if present as K280i or Na2S04, it is soluble by the addition of suicient water and heated.

After the slurry or the crushed mass is delivered to the feed hopper I of the second kiln 8, it is heated to a temperature of from 480 C. to 770 C. to drive o* excess H2S04 which is accumulated in storage tank 9 from which it is delivered to the vat 5 for the digestive process hereinabove described. I'he S03 is also driven 01T and the iron sulphate is changed to insoluble iron oxide. The kiln for heating at these tempera` tures is preferably lined with glazed nre brick and the section of the kiln designated by the numeral 8a. is preferably provided with baflles I0 as shown in Fig. 2, which function to agitate the material to expose it to the flame from the burning end of the kiln to assure complete change ofl soluble Fe2(SO4) a to insoluble Fe20a. The material is fed into the vats I I and suicient water is added to the finely ground mass and heated to make all the A12 S04)2 soluble. Any K2S04 or Na2S04 present also becomes soluble. The insoluble residue containing Si02, FezOs, Ti2(S04)3 and K2OA12036S102 0I' NazOAlzOaGSOz are removed from the soluble 'parts either by lter press l2 or by any other suitable method of extraction. The soluble part is evaporated to a solid mass either as crystals or powder in the evaporators I3. It is not necessary to remove all the excess water at this point, as any excess will be driven off in kiln I5. It is then delivered to the feed hopper I4 of the third kiln I5 Where it is heated to a temperature above 770 C. for a sufficient time to drive off all the S03 in the soluble A12(S04)3. This step changes the A1203 in the soluble Al2(S04)3 to the insoluble A1202.

If no small amounts of K280i or Na2S04 or Ti2 S04 3 are present, the A1203 will be in a commercially pure state. Should any of the above enumerated elements be present, they may be leached out by the addition of water and heated in the vat I6. The insoluble A1203 is removed from the material by a lter press or in any other suitable way and any water present with the A1203 is driven 01T. If K2SO4, Na2SO4 0r T2(SO4) 3 are present with the A12 S04)3, the mass should be heated to a temperature to exceed 1000 C. to vaporize all of the K2S04 or Na2S04, leaving the pure A1203.

The above method of recovering pure aluminum oxide from calcined clay bodies or the like, or from slags, is more efcient than that disclosed in my earlier issued patent, which is particularly useful for recovering aluminum oxide from alunite ores.

Although one embodiment of the invention has" been illustrated and described, it will be evident to those skilled in the art that various modications may be made in the details thereof, such as the kind of acid used in digestion of the ore compounds, without departing from the principles herein set forth.

I claim:

1. The process of treating alumina bearing ores and the like which comprises the steps of crushing, grinding and screening the ore and passing it to a kiln, calcining the screened ore at temperatures between 300 C. to 900 C., adding sulphuric acid of a concentration of at least 30% to digest the calcined material to change A1203 to soluble A12(S04)3, and the iron or titanium oxides to soluble sulphates, passing the digested product to a second calcining kiln, treating it at a temperature of from 430 C. to 770 C. to drive off excess H2S04 and S03 to change Fe2(S04)3 to insoluble Fe203, adding water and heating to dissolve all A12(S04)3, K2S04 and Na2S04, removing the insoluble residue, evaporating the soluble parts to a solid mass as crystals or powder, passing the soluble parts to a third kiln, heating it to a temperature above 770 C. to drive off all S03 to change A12(S04)3 to insoluble A1203, adding water to leach out K250i, Na2S04 and Ti2(S04)2 if present, and removing the insoluble A1203.

2. The process of treating alumina bearing ores and the like which comprises the steps of crushing, grinding and screening the ore and passing it to a kiln, calcining the screened ore at temperatures between 300 C. to 900 C., adding sulphuric acid of a concentration of at least 30% to digest the calcined material to change A1203 to soluble A12(S04)3, and the iron or titanium oxides to soluble sulphates, passing the digested product to a second calcining kiln, treating it at a temperature of from 480 C. to 770 C. to drive off excess H2S04 and S03 to change Fe2(S04)a to insoluble Fe203, adding water and heating to dissolve all A12 S04)3, K2S04 and Na2SO4, removing the insoluble residue, evaporating the soluble parts to a solid mass as crystals or powder, passing the soluble parts to a third kiln, heating it to a temperature above 1000 C. to vaporize K2SO4 and Na2S04, leaving pure A1203.

ROBERT C. HAFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,233,977 Cameron July 17, 1917 1,388,436 Moldenke Aug. 23, 1921 2,398,425 Ha Apr. 16, 1946 

1. THE PROCESS OF TREATING ALUMINA BEARING ORES AND THE LIKE WHICH COMPRISES THE STEPS OF CRUSHING, GRINDING AND SCREENING THE ORE AND PASSING IT TO A KILN, CALCINING THE SCREENED ORE AT TEMPERATURES BETWEEN 300* C. TO 900* C., ADDING SULPHURIC ACID OF A CONCENTRATION OF AT LEAST 30% TO DIGEST THE CALCINED MATERIAL TO CHANGE AL2O3 TO SOLUBLE AL2(SO4)3, AND THE IRON OR TITAMIUM OXIDES TO SOLUBLE SULPHATES, PASSING THE DIGESTED PRODUCT TO A SECOND CALCINING KILN, TREATING IT AT A TEMPERATURE OF FROM 480* C. TO 770* C. TO DRIVE OFF EXCESS H2SO4 AND SO3 TO CHANGE FE2(SO4)3 TO INSOLUBLE FE2O3, ADDING WATER AND HEATING TO DISSOLVE ALL AL2(SO4)3, K2SO4 AND NA2SO4, REMOVING THE INSOLUBLE RESIDUE, EVAPORATING THE SOLUBLE PARTS TO A SOLID MASS AS CRYSTALS OR POWDER, PASSING THE SOLUBLE PARTS TO A THIRD KILN, HEATING IT TO A TEMPERATURE ABOVE 770* C. TO DRIVE OFF ALL SO3 TO CHANGE AL2(SO4)3 TO INSOLUBLE AL2O3, ADDING WATER TO LEACH OUT K2SO4, NA2SO4 AND TI2(SO4)3 IF PRESENT, AND REMOVING THE INSOLUBLE AL2O3. 